A silicon-cast device that aids in securing rope ends by
ensuring a figure-eight knot is tied for use in gym and rock
climbing
By:
Shane M. Treadway
SUBMIITED TO THE DEPARTMENT OF MECHANICAL ENGINEERING IN
PARTIAL FULFILLMENT OF THE REQUIREMENS FOR THE DEREE OF
BACHELOR OF SCIENCE IN MECHANICAL ENGINEERING
AT THE
MASSACHUSETTES INSTITUTE OF TECHNOLOGY
JUNE 2008
Copyright 2008 Shane M. Treadway. All rights reserved
The author hereby grants M.I.T. permission to reproduce
and to distribute publicly paper and electronic
copies of this thesis document in whole or in part
in any medium now known or hereafter created.
Author
-
Department of
/
hanical Engineering
May 9th 2008
Certified by-_
Alex Slocum
Professor of Mechanical Engineering, ESG Director, MacVicar Fellow
Thesis Supervisor
_,-Accepted by_
MASSACHLSTTS INSTI
OFTEOHNOLOGY
AUG 14 2008
UBRARIES
E
,
.Chairman,
ARCHNES
John H. LienhardV
Sessor of Mechanical Engineering
Undergraduate Thesis Committee
A silicon-cast climbing device that aids in securing rope ends by ensuring a figure-eight
knot is tied for use in all forms of climbing
by
Shane M. Treadway
Submitted to the Department of Mechanical Engineering
On May 9, 2008 in partial fulfillment of the
Requirements for the Degree of Bachelor of Science in
Mechanical Engineering
Abstract
Between the years of 1953 and 2005, there were 253 fatalities from rappel
failure/error. Some of these deaths may have been prevented if a stopper knot was tied at
the end of the rope. Current climbing habits do not reinforce the tying of a stopper knot.
More people are learning to climb in the gym and do not know risk reducing habits when
beginning to climb outside, such as tying a stopper knot. The Hedgehog is a silicon
device that reinforces the risk reducing habit of tying a stopper knot by a combination of
form and color. A specially designed form aids in correct knot tying and the color signals
the climber their attention is needed. When the Hedgehog was given to climbers in a
climbing gym and had a success rate of 70%. Climbers without the Hedgehog had a
success rate of only 8%. Success was defined as having a stopper knot in the rope when
the climber began to ascend the route.
Thesis Supervisor: Alex Slocum
Title: Professor of Mechanical Engineering, ESG Director, MacVicar Fellow
Co-Advisor: Dave Custer
Title: Lecturer, ESG/WHSP
Table of Contents
2
............................................
Abstract
3
Table of Contents .......................................................................................................
4
.........................................
Introduction
Lowering and Rappelling.................................................. ....................................... 5
7
Climbing Gym s vs. Outdoors ............................................................. ...................
8
Solution... ................................
9
Background ................................................................................................................
9
Standards...................................................
10
Functional Requirem ents ............................................................... ..........................
10
Easy to use .................................................................................................................
Quick to inspect............................................................................................................ 11
Does Not Fail............................................................................................................... 11
12
Prototyping ...................................................
Form Selection ................................................... .................................................... 12
Designing the Form .................................................................... ........................... 13
MaterialSelection ................................................ .................................................. 15
Mold Creation.............................................................................................................. 15
Final Prototype................................................................................................................ 17
Testing in a gym .................................................. ................................................... 18
Conclusions ...................................................
18
Future Work................................................................................................................. 19
Bibliography .................................................................................................................... 20
Introduction
A silicon cast knot-guiding device that prevents the rope end from slipping
through a belay device would help teach better climbing practices by signaling climbers
when the rope end is tied off and therefore secure. The importance of securing rope ends
is evident in "Accidents in North American Mountaineering'"' that reports 10 accidents
due to rappel failure/error in the outdoors in 2007 and 252 since 19531. Two of the
accidents 2 involved the rope slipping through the belay/rappel device (BRD). These
accidents could have been prevented if a stopper knot (Figure 1) was tied near the end of
the rope. The knot stops the rope from slipping through the belay device by jamming it
(Figure 2). The problem is making climbers aware off the need to secure the rope ends.
My solution is to use a silicon cast knot-guiding device that will be called The Hedgehog
from hereafter. The Hedgehog is a silicon device that reinforces the risk reducing habit of
tying a stopper knot by a combination of form and color. A specially designed form aids
in correct knot tying and the color signals the climber their attention is needed.
Figure 1: Typical rappel device setup with a
figure eight stopper knot tied in the end
Figure 2: Figure eight stopper knot jammed in
a belay device
1Accidents due to rappel/failure or error include many different things such as the
equipment, rappelling carelessly, and many others.
anchor failing, incorrect use of rappelling
2 Not all of the accidents are written up and there may have been more cases where
the rope slipped through the BRD.
Lowering and Rappelling
There are two climbing activities where rope ends need to be secured. The rope
can slip two ways through a BRD while lowering or rappelling. Lowering involves a
belayer and a climber (Figure 3). The climber reaches the top of the route and the belayer
lowers him to the bottom. The second area in which accidents can occur is rappelling
(Figure 4). This method is used by climbers to descend a cliff or route by rappel stations
that someone else has placed. Both methods involve an anchor point, BRD, and a rope.
These two methods of descent allow you to clean an anchor3 and reach the ground.
Figure 3: The climber on the left is being lowered Figure 4: A person rappelling down a cliff-face
3Cleaning an anchor involves retrieving your gear from the top of a climb so you can use
it again. The bolts that you clip into are
permanently left.
Lowering is one way to get off a route for most single pitch climbs that are less
than half a rope length. Lowering involves a belayer and climber where the belayer is in
control of the climber's descent. Figure 5 shows several scenarios that may occur during
lowering. The variable in the figures is the length of the rope and accidents occur when it
is not the proper length. Belayers manage the control of the descent with a BRD that
gives the belayer a mechanical advantage allowing them to hold a climber with less than
100 N of force. Lowering may be done during top roping or cleaning a route.
A
B
C
D
Figure 5: Possible occurrences for lowering
A) A typical configuration when the climber wishes to descend B) The climber safely reaches the ground
C) The rope is too short and the climber falls to the ground D) The rope is too short but the Hedgehog
prevents the rope from going through the BRD
A climber ascending routes that are more than a rope length may have to rappel 4
to reach the ground. Rappelling is used to descend and involves anchoring the rope at a
preset Point A and then lowering yourself with a belay device to another preset Point B .
Guidebooks to climbing areas give information about them but finding the rappel points
on a wall after seeing them in a book is often difficult, especially if you are looking for
them while you are rappelling.
Rappelling involves a BRD device, and similar frictional advantages, that allows
the climber to control their descent down the rope. Ropes are made in various lengths of
4Rappelling also allows the climber to lower off the anchor without causing wear on it
50, 60, and 70 meters and the route length depends on the anchor setup. Figure 6 shows
how rope length and configuration affect the climber's rappel.
Anchor
-- 0
30m
Rope 50m
Rope 60m
-III //
/ /
Rope 50m
I
B
B
D
E
Figure 6: Possible occurrences for repelling
A)Atypical configuration found on routes B)Correct rope length and placement
C) Correct rope length but bad placement D) Short rope with good placement
E) Device Placement to prevent an accident in C or D
To prevent the failure mode in which the rope end runs through the BRD the
Hedgehog both ends of the rope must have knots in them. The Hedgehog will help
climbers manage risks by reminding them to secure the rope ends with a correctly tied
stopper knot. The red color of The Hedgehog will serve as a reminder to either the
climber or their partner that the rope ends need to be secured. Rappelling may occur at
the end of the day when people are tired or anxious to be finished and a small reminder
can help the climber secure the rope.
Climbing Gyms vs. Outdoors
Alerting climbers to the importance of securing rope ends is of special importance
when they learn how to climb in a gym. The easiest time to teach someone safety is when
he or she is first learning about it. Making the transition from climbing in a gym to
climbing outside involves learning several new techniques and it is helpful to learn as
many in a gym as possible. Climbing gyms are user-friendly so climbers may climb as
quickly as their ability allows. Anchors are set up on climbs, the ropes are in place and of
the correct length, there is no need to rappel, and staff supervision walking around to help
manage risk. This can lead to a relaxed attitude regarding risk management because the
gym is setup for you to climb quickly without worrying about other issues. Climbing
outside requires the climber to make sure they are managing risk at all times. A climbing
gym involves less rappelling than in the outdoors. If you set lead climb or top-rope in a
gym, you are lowered to reach the ground. Climbing outdoors requires you to retrieve
your gear from the top of a climb that necessitates rappelling.
So climbing outside involves more variables. In addition to tying in, climbing,
leading, belaying, and lowering, you may have to setup an anchor, rappel, and find the
route. If you learn to climb in a gym, then your exposure to rappelling is lower which
may lead to mistakes rappelling outdoors if you do not get proper instructions. The
Hedgehog is a means to aid in teaching techniques to help manage risk during rappelling.
Solution
The Hedgehog is designed to aid in securing rope ends by reminding people they
need to tie a stopper knot and guiding them so that the stopper knot is correctly tied. If a
person has learned to climb in a gym then they are less likely to be aware of all the risk
management techniques. It is a different mindset when you are climbing indoors as
opposed to outdoors. The Hedgehog is of particular importance to climbers that are
making the transition from climbing in the gym to climbing in the outdoors.
Teach the correct initial technique of risk management during rappelling is not the
main goal of the Hedgehog. People that have just learned to rappel and people that have
rappelled many times still need to remember to tie the stopper knot. The knowledge of
how to tie it does not mean that the climber will tie it. The bright red color of The
Hedgehog will help grab climber's attention and remind them something needs to be
checked, while its molded shape conforms to a properly tied figure eight and helps guide
the tying.
Background
Climbing is inherently dangerous and climbing standards try to mitigate the risk
wherever possible. There are requirements that some climbing gear must have to be
issued in the United States, and there are some unofficial practices people follow to help
reduce risk. These official and unofficial practices are what helped guide me in making
my device. I also used a general guide" for Product Design that allowed me to focus on
the ergonomics of the Hedgehog.
Standards
There are international standards for ropes and critical climbing equipment for
strength and durability. There are also unofficial standards that people seem to follow.
Redundancy is used at critical points such as two bolts at an anchor. The color red also
signals that a device has not been secured. Some harnesses have a strip of red on their
buckle to show when you have not double backed the waist strap to secure it (Figures 3 &
4). Some locking carabineers have red on the gate when they are unlocked. Locking the
carabineers causes the red strip to be covered. A review of an outdoor store, REI, found
that four of their locking carabineers used a red color to signal when they gate was
unlocked. Only two harnesses showed a strip of red when they were unbuckled, this small
number may be because many of the newer harnesses removes the need to buckle them.
Figure 7: A harness buckle showing red tape
that has not been secured
Figure 8: A harness buckle that has been
doubled back and secured
Functional Requirements
The characteristics for the Hedgehog were based primarily on its safety and then
its usability. A concern during the creation of the Hedgehog was that people should not
mind using it and remember to use it without becoming aggravated during climbing.
Climbing involves a series of checks before belaying starts and the hope is that the
Hedgehog will help climbers secure the ends of the rope as part of that checklist.
Easy to use
The Hedgehog needs to be easy to use without an instruction manual. People
should be able to see it and know how to use intuitively, see row 1,Table 1. A climber
should be able to pick it up after a minute figure out how it works. Actual use of the
device should require less than 10 seconds. The Hedgehog was designed to fit into an
average man or woman's palm so they can hold it without discomfort. It does not require
any motions to tie the knot beyond holding the rope down while the outline is followed.
Quick to inspect
The Hedgehog relies on color and interaction in order to be effective. The device
is clear with a red color along the rope's path, see row 2, Table 1. With this coloring
system, someone can quickly look at the Hedgehog and tell whether the figure eight is
tied correctly by checking for any red spots on the device. A clear device with the rope
tied around it is correctly tied. This ensures that someone does not tie a knot that could
come undone when the device is loaded. The red coloring also follows similar guidelines
in climbing that were mentioned above. It allows either the climber or belayer to see the
device when they are performing their safety checks.
Does Not Fail
The success rate of preventing the rope ends from feeding through the BRD for
the Hedgehog equals that of a regularly tied figure eight. Figure eights have been shown
to hold under static loads of 1400 kg on a static rope"'. However, if the knot is tied with
only several inches left on the end it can untie itself under stress because of rope slippage.
The Hedgehog will provide extra friction in the knot to help increase the success rate.
Additionally, when the figure eight knot is loaded the scorpion should not extrude into
the belay device causing it to stick or otherwise rendering the belay device unusable.
Row 3 table 2 shows further countermeasures for this situation.
Table 1: Design Criteria
FR
Quick to
use
DP
Only one
threaded point
Analysis
Ref.
Belayer should
be able to use
the device in
less than 5
seconds
Past
Experience
Risks
The belayer
uses it
incorrectly
because it is
quickly
configured
Counter
measures
Have a picture on
the device
showing how is
should be used,
or something
similar
Prototyping
There were several stages required for the production of the prototype Hedgehog.
The first step was creating a pattern that would fulfill the functions specified. It needed to
take into account safety, ergonomics, and usability. Next, a material was selected that
would be used for the cavity and casting of the final mold. The materials ended being
used were a two-part urethane for the cavity and a two-part silicon for the mold.
Form Selection
The first decision that needed to be made was what form the Hedgehog was going
to aid in people securing the end of the rope. It needed to be simple and small so the
climber could carry it with them at all times, Figure 9 was an early prototype. Based on
this initial idea I concentrated on a hand held device as opposed to ground-based stations.
Rappel devices similar to a prusik 5 were also excluded because of complexity and time
requirements.
Figure 9: Initial prototype pattern
Designing the Form
When designing the Hedgehog shape safety was considered first and then
usability. Ensuring the figure eight knot was tied correctly directed the shape of the
Hedgehog. The Hedgehog is designed so that the climber must follow the outline of the
rope around the device. The climber knows that the rope is tied correctly when they
should only see green because the rope is covering all of the red on the device. Other
methods were discarded because they were not as clear to the climber that the rope was
tied correctly.
5A friction hitch used as a backup belay device that halts your descent if your hands leave the rope due to an accident or the need
to
retrieve gear from a route or other reason
The figure eight knot can be tied two different ways. Rather than dealing with
both of these variations, there is an arrow and rope-guide section near the bottom of the
Hedgehog. This forces the user to tie the figure eight with a right-handed chirality. The
Hedgehog is designed to fit in the palm of a hand so climbers can easily hold the device
and tie the knot with both hands. Keeping the knot from becoming untied relies on three
retainers within the Hedgehog. There is the previously mentioned rope guide and two
more edges on the bottom and top. These edges on the top and bottom are able to hold the
rope because they are inset from the natural contours of the knot. There is a hole for end
of the rope to be threaded. Table 2 shows the major ideas that were being considered
when designing the Hedgehog.
Table
2:
--- '---~----Prototvne Criteria
FR
end of the
figure 8
knot
DP
threads through
a hole
Analysis
Ref.
Risks
Counter
measures
not exert
enough force
to deform the
mold (<800
psi shear)
ATC belay
device
knot incorrectly
guides that help
direct the knot
The threaded point allows the end of the knot to be clearly marked to help ensure it is tied
correctly. There are not two threaded points for the beginning and end of the knot
because it takes too long to untie. Figure 10 was an early idea that required 6 threaded
points and helped influence the final use of only one.
Figure 10: Early Completely threaded design
Material Selection
Silicon is used to cast the climbing device because it is lightweight, provides a
static coefficient of friction of 0.4, and has a shore hardness of 40-A. The device needs to
be lightweight to encourage climbers to carry it around on their harness. Enough friction
is needed to ensure the knot does not slip out of the tied form. The Hedgehog should
provide at least the same friction as rope on rope and preferably more to keep the knot
from coming untied. A shore hardness of 40-A allows the Hedgehog to be durable and
keep the load on the knot instead of the structure of the device.
Mold Creation
The pattern was made using Crayola Magic mold. This material did not give as
much definition as was desired but the other alternative of modeling clay was not pliable
enough for the shape. No tools were required for pattern except for a short piece of rope.
The pattern dried for 24 hours before it was used to create the cavity. The cavity
compound was OOMOO 30, a platinum catalyzed two-part silicon compound. Figure 11
shows all the materials required for creating a mold.
Figure 11: Three initial designs created for possible prototyping and required materials
The pattern was secured to the bottom of a small box and both the pattern and box
were sprayed with a release spray. The cavity compound was poured in around it and
allowed to set for 6 hours. After setting the cavity, the pattern was removed and allowed
to dry for another hour. Release spray was applied to the cavity. A silicon mixture, SortaClear 40, was mixed for the mold. Vacuum degassing was used for 10 minutes to take out
the air bubbles that occurred from mixing. After pouring the mold, it was allowed to sit
for 16 hours before being removed.
Final Prototype
All of the prototypes were cast out of Sorta-Clear 40, a two-part silicon. The
initial cavity mold was made out of OOMOO 30, a two-part silicon mixture, and the
second cavity mold was made from The Hedgehog Skin, a two-part urethane mixture.
The initial mold did not set well and the edges in contact with the cavity were still sticky
after it had set for the required amount of time. This was probably due to both the mold
and the cavity having a silicon base. The second mold was slightly sticky but after sitting
in the air for 12 hours after being demolded, they finished setting. A third mold was cast
with green dye but it did not cast successfully. The green dye or the age of the casting
material may have caused the improper setting. The second mold was modified to look
like the desired product and used for testing purposes, Figure 12. The rope fit well into
the molded outline of the final design, Figure 13, and little of the coloration showed when
it was properly tied. Several variations were tried where the rope was tied incorrectly and
the color showed up well.
Figure 12: Final prototype
•1
fis
Filgure 1j: kinal prototype with a stopper knot tied
Testing in a gym
Observing people tie figure eights without the Hedgehog at a climbing gym
showed an average time of 4 seconds with 8 people. 6 These climbers were then asked to
tie the figure eight using the Hedgehog7 and had an average time of 6 seconds. Three
climbers that had been climbing only once before had an average tying time of 9 seconds
without The Hedgehog and 13 seconds with the Hedgehog. Observing 6 people in the
gym for an hour showed only one person look at or physically check the end rope to see
if a stopper knot was tied. I let three people use The Hedgehog for an hour at a time and
out of 13 climbs completed, the belayer remembered to use the device 10 times. The
three times it was not used was towards the end of the hour and the Hedgehog was left on
the rope at the previous climb.
Conclusions
The Hedgehog had a success rate 70% between a combination of color and
observance by their partners. Several times the climber remembered to tie the stopper
before they started climbing. However, the majority of times either the climber or the
belayer was reminded to tie the stopper knot during routine safety checks. The red color
on the device may have helped grab attention but the device itself seemed to help people
more. The red color may help people when they are climbing outside and climbing
normally. An hour may not have been enough time to relapse into normal climbing
habits.
6All
of the climbers had been climbing at least two times before
7 The first three times they used the device were not counted in the above time
It was interesting to note that the Hedgehog was not used when it was forgotten at
the previous climb. In the gym, this may be a problem because you are using different
ropes. A way to help climbers in the gym remember the Hedgehog may be to have a
colored carabineer that attaches to the Hedgehog. This way if they forget the Hedgehog
they will still have the carabineer to remind them at the next climb. This seems a little
excessive but in a climbing gym, there are plenty off ways to help people remember
something. Climbing outside people normally have their own ropes and so this would not
be a problem.
Future Work
The testing was only carried out in a climbing gym among people that were
familiar with climbing. More testing would be desired among inexperienced climbers
indoors and among climbers in both lowering and rappelling outdoors. It would also be
interesting to see if several of the devices could be used in a climbing gym to see the
effect on other people. If there were multiple devices in a climbing gym other people may
start tying the stopper knot as well from others doing it.
A solid model of the pattern would be much easier to make incremental changes
now the general form is finalized. It would also allow more detailed texturing and
labeling of the design. The texturing of the Hedgehog where the rope touches it helps
define how knot should be tied. A series of numbered arrows with labels could help guide
people that are unfamiliar with tying a figure eight and it would help people that are using
the Hedgehog for the first time.
Bibliography
i) Williamson, E., John, (2005). Accidents in North American Mountaineering.Golden,
CO: The American Alpine Club, Inc.
ii) Ulrich, T., Karl, (2004), 3rd. ProductDesign andDevelopment. New York, New
York: McGraw-Hill/Irwin.
iii) Cliffe Steve: Sheehan, Alan. Vertical Rescue (VR) Equipment Load Testing Report.
May <oberon.ses.nsw.gov.au/resources/EquipmentTesting-KiamaVRPDW.pdf>